Power-save method for 802.11 multicast paging applications

ABSTRACT

A power-save method for a network with an access point and an associated power-save client. The access point buffers wireless data that includes a unicast frame and a multicast frame. A periodic scheduled beacon message is transmitted with a unicast indication element and a multicast indication element. The unicast element instructs a client to remain awake to receive a buffered unicast frame, which includes a destination MAC address. The multicast element instructs a client to remain awake following the beacon to receive a buffered multicast frame, which includes a destination multicast address designating a multicast group of which the client is a member. At least one beacon message is designated as a multicast delivery beacon. The buffered multicast frame is transmitted following the designated multicast beacon. The multicast element contains a list of entries, each entry corresponding to either a multicast MAC address, multicast IP address, or client identifier.

RELATED APPLICATION

The present system is related to U.S. patent application Ser. No.10/723,328 by Griswold, et al. entitled “OPTIMIZING 802.11 POWER-SAVEFOR IP MULTICAST GROUPS” filed on Nov. 26, 2003, the entirety of whichis hereby incorporated by reference.

BACKGROUND

The present invention relates generally to wireless broadcasttransmissions and more particularly to a method for power consumption byan IEEE 802.11 client station containing both a Voice-over-InternetProtocol and an Internet Protocol paging application.

An IEEE 802.11 client station having both Voice-over-Internet Protocol(VoIP) and Internet Protocol paging applications must receive unicastVoIP messages, broadcast Address Resolution Protocol, or ARP, messages,and IP Multicast “paging” messages. In a typical computer network,unicast VoIP operation is a communications transmission between a singlesender and a single receiver over a network.

In contrast to the unicast transmission of VoIP, paging is typically amulticast operation. Multicast is a technique that allows data,including data encapsulated in packet form, to be simultaneouslytransmitted to a selected set of destinations. Some networks, such asEthernet, support multicast by allowing a network interface to belong toone or more multicast groups. In some applications of multicast,identical data is simultaneously transmitted to a selected set ofdestinations in a network, without obtaining acknowledgement that thetransmission was received by the recipient devices. Multicasttransmissions are also capable of being sent to a multicast address,which is typically a routing address that is used to address, i.e.,designate, simultaneously all the computers in a group and usuallyidentifies a group of computers that share a common protocol, as opposedto a group of computers that share a common network.

Thus, while multicast has a single sender and multiple recipients,unicast has but a single sender and a single recipient. Similar tomulticast, broadcast operation is the transmission of signals that maybe simultaneously received by stations that typically make noacknowledgement of the receipt of the transmission.

Address Resolution Protocol is a communications protocol used to map aselected Internet Protocol (IP) address to a preset Media Access Control(MAC) address. ARP matches higher-level IP addresses to the physicaladdresses of the destination host. It uses a lookup table (called an ARPcache) to perform the translation. When the address is not found in theARP cache, a broadcast is sent out on the network with a special formatcalled the ARP request. If one of the machines on the network recognizesits own IP address in the request, it sends an ARP reply back to therequesting host. The reply contains the physical hardware (MAC) addressof the receiving host. The requesting host stores this address in itsARP cache so that all subsequent datagrams to this destination IPaddress can be translated to a physical address.

A Traffic Indication Message (TIM) may be found in an 802.11 BeaconFrame which is transmitted from an 802.11 access point (AP). In essence,a TIM is used by access points to tell power-save client devices thatone or more unicast packets are waiting for them. A TIM consists of anarray of bit flags, with one bit flag for each client associated withthe AP. An AP sets a station's TIM bit to “1” if it has one or moreframes buffered for the client. An AP sends Beacons at fixed intervals.If an 802.11 power-save station only needs to receive unicast frames, itcan wake up to receive a Beacon, check its TIM bit, and immediatelyreturn to a “sleep” mode if the TIM bit is set to “0”.

A Delivery Traffic Indication Message (DTIM) is contained in DTIMBeacons sent by access points. If a power-save station associated withan AP, then the AP buffers broadcast and multicast frames and sends thebuffered frames to associated stations immediately following a DTIMBeacon. If a power-save station must receive broadcast or multicastframes, then it must wake up for each DTIM Beacon transmission and itmust stay awake until the last broadcast/multicast frame is transmitted,following the DTIM Beacon.

Proxy ARP refers to a method wherein an AP sends an ARP Reply, on behalfof an associated station, when the AP receives and ARP Request directedto the associated station. Proxy ARP enables a power-save station tosleep during the broadcast/multicast period, following a DTIM Beacon, ifit does not need to receive any of other multicast or broadcast frames.

Previous attempts to implement proxy ARP 802.11 VoIP phone applicationshave been met with limited success. Such uses of the proxy ARP hasenabled the VoIP phone to sleep, or operate in power-save protocol mode,during lengthy broadcast/multicast transmissions. However, thismechanism, by itself, is not usable for an 802.11 VoIP/Paging deviceinsofar as the paging application requires the phone to remain activefollowing the DTIM to receive other multicast transmissions.

A problem associated with an 802.11 client device supporting both VoIPand paging applications is that the radio power consumption in an 802.11VoIP phone is much higher than the radio power consumption in a cellulartelephone. The greater drain on energy has limited the application ofboth VoIP and paging into a single device. Power-save stations must stayawake, for the duration of the multicast delivery period, to receivemulticast transmissions. As a result, broadcast/multicast transmissionscan reduce battery life in power-save stations.

Thus, there exists a need for a system and method to provide aneffective power-save solution for combined VoIP/paging applications.

SUMMARY OF INVENTION

The present innovation addresses the above-noted deficiencies andothers, and teaches a system and method for facilitating power-savingsin an IEEE 802.11 VoIP/Paging device.

In accordance with the present invention, there is taught a power-savesystem for wireless data transmission. The access point stores a list ofIP multicast addresses for each associated station, wherein each addressin the list corresponds to an IP multicast group. The access point alsomaintains a set of IP multicast groups, wherein each multicast group inthe set is identified by an IP multicast address. At least one stationassociated with the access point is a member of each of the multicastgroups in the access point's set of multicast groups. Each multicastgroup is classified as either “active” or “power-save”. An access pointclassifies a multicast group as “active” if all stations in themulticast group are operating in active mode; otherwise, the APclassifies a multicast group as “power-save” if at least one station inthe multicast group is operating in power-save mode. On 802.11 links, anaccess point transmits multicast packets, which are destined to anactive multicast group, immediately; an access point buffers multicastpackets, which are destined to a power-save multicast group, until thenext delivery traffic indication message (DTIM) Beacon; and an AP doesnot transmit multicast packets, which are not destined to an active orpower-save multicast group.

The access point includes a multicast traffic indication message (MTIM)element in each transmitted DTIM Beacon. The MTIM element comprises alist of zero or more entries. The MTIM element identifies power-save IPmulticast groups, for which downlink multicast frames are buffered inthe access point. When a power-save station is a member of an IPmulticast group identified by an entry in the MTIM element, the stationmust remain active to receive all power-save multicast transmissionssent following the DTIM Beacon.

In one aspect of the present system, the MTIM element is comprised of alist of zero or more IP multicast addresses. In another aspect of thepresent system, the MTIM element is comprised of a list of zero or moremulticast MAC addresses, where each MAC address corresponds to an IPmulticast address. The multicast MAC address is suitably generated byconcatenating a 3-byte hex 01005E prefix with the low-order 3-bytes ofthe multicast IP address. In yet another aspect of the present system,the MTIM element is comprised of a list stations that must stay awake,following a DTIM Beacon transmission, to receive multicasttransmissions. The list of stations in the MTIM element can bestructured as an array of bit flags, where each MTIM bit flagcorresponds to the association identifier of a station and the AP setsthe MTIM bit flag for a station to ‘1’ if the station is participatingin a multicast group where multicast frames are buffered fortransmission following a DTIM Beacon.

Still another aspect of the present system is the MTIM element notifiesthe station in an IP multicast group to stay active following thetransmission of the delivery traffic indication message to receivedownlink multicast frames buffered for the IP multicast group. Still yetanother aspect of the present system is the MTIM element notifies theassociated station that the access point supports the MTIM method andenables the associated station to selectively ignore useless multicasttransmissions.

A further aspect of the present system is the combination of themulticast traffic indication message element with an existing Proxy ARPmechanism, to provide an effective power-save solution for combinedVoIP/Paging applications. Further in accordance with the presentinvention, there is taught a power-save system for wireless datastreaming. The system includes an access point that provides a wirelessdata link to at least one associated client. The access point is placedin wired data communication with a data network. The access pointincludes memory that stores an IP address and MAC address for eachassociated client station. The access point further includes memory thatstores a list of enabled IP multicast addresses and a MAC address foreach associated client station. The system also includes registrationmeans adapted for registering each associated client with the accesspoint. The system includes means adapted for registering IP groupmembership information of each associated client with the networkinfrastructure. The system incorporates a receiver associated with theaccess point, the receiver including means adapted for receiving a datastream from the selected data network. The system further includes meansadapted for selectively notifying each associated client station of thedata stream according to the relationship data. The access point thenforwards the data stream from the access point to each notifiedassociated client. The system also includes link maintenance meansadapted for communicating link data between the access point and theassociated client. The link data represents an ongoing, active wirelessdata streaming link between the access point and the associated client.

One aspect of the present system is that the data stream includes VoIPand paging data. Another aspect of the present system provides that thelink maintenance means further includes a system adapted forcommunicating pending multicast transmissions to client stations. In yetanother aspect of the present system, the access point includes meansadapted for determining membership of each associated station in astreaming multicast data group.

Further in accordance with the present invention, there is taught apower-save method on a selected network comprising an access pointadapted to provide wireless data link to at least one associated client,the access point adapted to be placed in wired data communication withthe selected network. The access point stores, in an associated memory,an IP address and a MAC address corresponding to each associated client.The access point stores, in an associated memory, a list of multicastaddresses and a MAC address corresponding to each associated client.Each client is registered with the access point. Relationship dataassociating a MAC address, an IP address, and a list of multicastaddresses, for each registered client is stored in the memory. Theaccess point receives a data stream from the selected data network. Theaccess point then selectively notifies each associated client of thedata stream according to the relationship data. The access point signalsa client when it has one or more pending multicast transmissions,wherein the destination multicast address is in the client's list ofmulticast addresses. The client then stays awake to receive themulticast transmissions.

One aspect of the subject invention is that a data stream includes VoIPand paging data. Yet another aspect of the present system is a teaching,wherein an access point determines membership of each associated stationin a streaming multicast data group.

Yet further in accordance with the present invention, there is taught acomputer-readable medium for wireless data streaming. The computerreadable medium includes an access point adapted to provide a wirelessdata link to at least one associated client, wherein the access point isplaced in wired data communication with a selected data network. Thecomputer-readable medium also includes means adapted for storing atleast one of IP address data and MAC address data for each associatedclient in a memory associated with the access point. Thecomputer-readable medium also includes means adapted for storing a listof multicast address and a MAC address for each associated power-saveclient in a memory associated with the access point. Thecomputer-readable medium further includes registration means adapted forregistering one associated client with the access point. The accesspoint includes means adapted for storing, in the memory, relationshipdata associating a MAC address and IP address for each registeredclient. The access point includes means adapted for storing, in thememory, relationship data associating a MAC address and a list of IPmulticast addresses for each registered client. The computer readablemedium teaches means adapted for receiving, on a receiver associatedwith the access point, a data stream from the selected data network. Thecomputer readable medium also teaches means adapted for selectivelynotifying each associated client station of the data stream according tothe relationship data. The computer readable medium further includeslink maintenance means adapted for communicating link data between theaccess point and the associated client, wherein the link data representsan ongoing, active wireless data streaming link between the access pointand the associated client.

One advantage of the subject invention is that a data stream includesVoIP and paging data. Another advantage of the present computer readablemedium is in the teaching of a system for communicating link openinformation to the associated client. Yet another advantage of thepresent system is a teaching, wherein an access point determinesmembership of each associated station in a streaming multicast datagroup.

Still yet further in accordance with the present invention, there istaught a computer implemented power-save method for wireless datastreaming. An access point stores, in an associated memory, an IPaddress and a MAC address corresponding to each associated client. Anaccess point also stores, in an associated memory, a list of IPaddresses and a MAC address corresponding to associated clients. Eachclient is registered with the access point. Relationship dataassociating a MAC address and an IP address for each registered clientis stored in the memory. Relationship data associating a list ofmulticast addresses and a MAC address for registered clients is alsostored in the memory. The access point receives a data stream from theselected data network. The access point then selectively notifies eachassociated station of the data stream according to the relationshipdata.

One advantage of the subject invention is that a data stream includesVoIP and paging data. Yet another advantage of the present system is ateaching, wherein an access point determines membership of eachassociated station in a streaming data group. Still yet anotheradvantage of the present system is the teaching of classification of thestreaming data group into either a power-save or active group.

Further in accordance with the present invention, there is taught apower-save method for a network with an access point and an associatedpower-save client. The access point buffers wireless data that includesa unicast frame and a multicast frame. A periodic scheduled beaconmessage is transmitted with a unicast indication element and a multicastindication element. The unicast element instructs a client to remainawake to receive a buffered unicast frame, which includes a destinationMAC address. The multicast element instructs a client to remain awakefollowing the beacon to receive a buffered multicast frame, whichincludes a destination multicast address designating a multicast groupof which the client is a member. At least one beacon message isdesignated as a multicast delivery beacon. The buffered multicast frameis transmitted following the designated multicast beacon. The multicastelement contains a list of entries, each entry corresponding to either amulticast MAC address, multicast IP address, or client identifier.

Still other advantages of the present invention will become readilyapparent to those skilled in this art from the following descriptionwherein there is shown and described a preferred embodiment of thisinvention, simply by way of illustration of one of the best modes suitedfor to carry out the invention. As it will be realized, the invention iscapable of other different embodiments and its several details arecapable of modifications in various obvious aspects all without from theinvention. Accordingly, the drawing and descriptions will be regarded asillustrative in nature and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of thespecification, illustrate several aspects of the present invention, andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a diagram illustrative of an IEEE 802.11 network;

FIG. 2 is a flow chart illustrating the Address Resolution Protocolaspect of the present invention; and

FIG. 3 is a flow chart illustrating the Multicast Traffic IndicationMessage of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following includes examples of various embodiments and/or forms ofcomponents that fall within the scope of the present system that areadvantageously used for implementation. Of course, the examples are notintended to be limiting and other embodiments may be implemented withoutdeparting from the spirit and scope of the invention. Specifically, apower-save station is suitably configured to eliminate the need to stayawake to receive all power-save multicast/broadcast frames sent by itsparent AP following a DTIM beacon.

As described herein, the present system and method has two primarycomponents:

I. Proxy Address Resolution Protocol (Proxy ARP), and

II. Multicast Traffic Indication Message (MTIM).

Each of the components are discussed separately and in detail below. Itwill be appreciated that the mechanisms described herein capable ofimplementation individually or combined. As well, an artisan willappreciate that the system and method described herein is not limited toIEEE 802.11 Voice-over Internet Protocol (VoIP) and multicast Pagingapplications. However, for convenience and demonstrative purposes, thedescribed embodiments are directed to a VoIP/Paging 802.11 application.

By way of background, FIG. 1 illustrates a simplified system diagram ofa typical network 100 in accordance with the present system and method.The network 100 includes wireless stations 105-130 suitably configuredand connected to access services and receive multicast transmission onthe network 100 via an access point 135. It will be appreciated that thewireless stations 105-130 are capable of transmitting and/or receivingdata packets via a wireless network such as any one of numerous wirelessdevices, including, but not limited to, a laptop/notebook portablecomputer having a Cardbus network adapter suitable for wirelesscommunication with a wired network, an electronic tablet having asuitable wireless network adapter, a handheld device or personal digitalassistant containing a suitable wireless network adapter forcommunicating to a wired network or the like.

The Basic Service Set (BSS) 140 of the access point 135 is shown.Wireless stations 105-130 are suitably configured to communicate withthe access point 135 so long as they remain in the BSS 140. In otherwords, as members of the BSS 140, wireless stations 105-130 arephysically located within the access point 135 wireless communicationcoverage area.

A backbone 145 is used to connect the access point 135 and a networkserver 150 via a physical wired connection 155. Typically, the backboneis a wired network connection such as Ethernet. An artisan willappreciate that any suitable means, wired or wireless, as well as anynetworking protocol known in the art, are suitably employed withoutdeparting from the spirit and scope of the present system and method.

During normal operation of the system 100, the network server 150 isused together with the access point 135 to authenticate wirelessstations 105-130. While the aforementioned network 100 illustrates asingle access point and six wireless stations, one of skill in the artcan readily appreciate that a network may comprise any number of accesspoints and any number or type of wireless stations.

It will be appreciated that the relative position of wireless stations105-130 may change with respect to each other and to the access point135. However, provided the wireless stations 105-130 remain within thecoverage area of the BSS 140, they will remain members of the BSS 140 ofthe access point 135.

In operation, an IP multicast stream 160 is received by the system 100from a remote location. It will be appreciated by one of ordinary skillin the art that a location of the sender(s) of the multicast stream 160is not particularly relevant to the present system. In other words, thepresent system and method is configured to operate as well with a localsender as with an extremely distant sender.

The wireless stations 105, 110 and 115 are suitably configured into amulticast group 165. As well, wireless stations 120, 125 and 130 aresuitably configured into a second multicast group 160. Of course, thegeneration of multicast groups is accomplished in accordance with theabove-referenced related U.S. patent application.

The wireless stations 105, 115, and 125 are configured to subscribe tothe multicast stream IP multicast stream 160 and are in active mode.Conversely, wireless stations 110, 120 and 130 shown are in sleep orpower-save mode. As illustrated, wireless stations 110, 120 and 130 arenot subscribers to the multicast stream IP multicast stream 160.

In accordance with earlier implementations, upon receipt of the IPmulticast stream 160 by the access point 135, the access point 135determines the mode, power-save or active, of all stations containedwithin the BSS 140. In this example, the access point 135 is suitablyconfigured to determine the mode of all stations in the individualmulticast groups 165, 170.

Wireless stations 110, 120 and 130 are in power-save mode while allremaining stations 105, 115 and 125 are operating in active mode. Inaccordance with earlier systems, because at least one station 110, 120or 130 is operating in power-save or PSP mode, the access point 135would automatically batch and queue all incoming multicast packets 160until the next Delivery Traffic Indication Message (DTIM) beacon is sentto the BSS 140.

However, in accordance with the method and system of the above-mentionedrelated application, the system is suitably configured to establishmulticast groups 165, 170 in order to streamline delivery of multicastmessages. In such circumstances, each individual group would adopt thecharacteristics of the BSS of earlier implementations.

I. Proxy ARP Power-Save Mechanism

Referring now to FIG. 2, there is shown the Address Resolution Protocolcomponent 200 of the present invention, wherein a Proxy ARP server issuitably configured to respond to address resolution requests targetedto an associated client station. As will be understood by those skilledin the art, ARP matches higher-level IP addresses to the physical (i.e,Media Access Control, or MAC) addresses of the destination host. When anIP address is not found in the ARP cache, a broadcast is sent out on thenetwork with a special format called an ARP request. When one of themachines on the network recognizes its own IP address in the request, itsends an ARP reply back to the requesting host. The reply contains thephysical hardware address of the receiving host. The requesting hoststores this address in its ARP cache so that all subsequent datagrams tothis destination IP address can be translated to a physical address.Proxy ARP enables an access point to respond to the ARP request for anassociated station in power-save protocol operation.

For explanatory purposes, FIG. 2 shows, via steps 205-235, the methodwherein the Proxy ARP server learns the associated client stationaddress. Beginning at step 205, the Proxy ARP server in the access pointdetermines whether it already has the address for the associated orassociating client. When the Proxy ARP server determines at step 205that the client address is known, the Proxy ARP server identifies IP/MACaddress bindings for the associated station at step 225. The skilledartisan will appreciate that the storage of the IP/MAC address bindingsenables the Proxy ARP server to properly function in accordance with thesubject method. It will be appreciated that any one of the 802.11 clientstations 105-130 will not need to receive broadcast ARP requests whenthe Proxy ARP server in the parent access point 135 is already aware ofthat client's IP address.

In the event that the Proxy ARP server has determined, at step 205, thatthe Proxy ARP server does not know the client address, the Proxy ARPserver then proceeds to step 210, wherein it is determined that theclient has not sent any IP packets or previously responded, through theaccess point, to an ARP request. A negative determination at step 210prompts the Proxy ARP server, at step 230, to snoop IP and/or ARPpackets sent by the client to gain knowledge of the client address. Forexample, the access point 135 automatically determines the IP address ofa client 105, by snooping IP and ARP packets sent by that client 105.After ascertaining the client address, the Proxy ARP server proceeds tostore the address in the IP/MAC address bindings for associated stationsat step 225.

When the client station has not sent any IP or ARP packets at step 210,the Proxy ARP server progresses to step 215, wherein the Proxy ARPserver determines that the client station has roamed from a previousaccess point to the current access point. Upon such a determination, theProxy ARP server proceeds to step 220, wherein the IP address associatedwith the client station is transferred from the old access point to thenew access point via a context transfer protocol. The IP address of anyor all of the wireless clients 105-120 are transferred from the oldaccess point 135 to the new access point, via the context transferprotocol when the wireless client or clients 105-120 roam from thecurrent BSS 140. Once the IP address has been transferred, the Proxy ARPserver proceeds to store the IP/MAC address bindings at step 225.

Returning to step 215, when the Proxy ARP server determines that theclient station has not roamed from a previous access point, the ProxyARP server gathers the client station IP address, at step 235, throughthe registration process with the parent access point by including an IPaddress element in an association or re-association message. Forexample, upon roaming from BSS 140 into a new access point's (not shown)BSS (not shown), wireless clients 105-120 register their correspondingIP addresses with their new parent access point by including an IPaddress in their association or re-association request messages. Uponreceipt of the client station IP address, the Proxy ARP server proceedsto store the IP/MAC address bindings at step 225.

Proceeding with the method illustrated in the flow chart of FIG. 2, theaccess point receives a broadcast ARP request on its Ethernet port atstep 240. The access point then, at step 245, searches its IP/MACaddress bindings for an IP address that matches the target IP addressembedded within the body of the ARP request. Upon the determination, atstep 250, that the access point cannot find a match for the target IPaddress in the IP/MAC address bindings it stores, the access point thendiscards the ARP request at step 255.

When the access point determines that a matching IP address is found atstep 250, the access point then determines whether a Proxy ARP server isresponding to the ARP request for the target IP address at step 260.When a Proxy ARP server is responsible for responding to ARP requestsfor the target IP address, the Proxy ARP server transmits an ARP replymessage with the MAC address corresponding to the target IP address, onits Ethernet link, at step 265.

If, at step 260, the Proxy ARP server determines that it is notresponding to the ARP request for an associated client station, theProxy ARP server translates the destination broadcast MAC address in theARP Request to the unicast MAC address that corresponds to the target IPaddress at step 270. The resulting unicast ARP request frame issubsequently forwarded, at step 275, to the target station as any other(e.g. power-save) unicast message. Upon receipt of the unicast ARPrequest, the target station generates an ARP Reply. For example, uponreceiving an ARP request targeted for station 105, the Proxy ARP server(not shown) within the access point 135 is configured to translate thebroadcast MAC address contained within the ARP request into a unicastMAC address corresponding to the target IP address in order to transmitthe message to station 105.

A power-save 802.11 station is not required to remain in an active stateto receive multicast/broadcast transmissions if i) the Proxy ARP serverwithin the access point is generating proxy ARP replies for the client;ii) the client does not have any other pending multicast messages, andiii) the client is aware of the proxy ARP service. In order tofacilitate the awareness of the client for the proxy ARP service, theaccess point is suitably configured to “advertise” that the access pointis providing the service via a Proxy ARP flag contained within aproprietary 802.11 information element. The proprietary informationelement is suitably included in an 802.11 Beacon and/or association orre-association response messages.

An artisan will appreciate that in accordance with 802.11 networkprotocol, a power-save VoIP station, in standby mode, must wake upperiodically to receive beacons, even if it does not need to receivemulticast/broadcast frames. In order to notify a station that it haspending multicast/broadcast messages, a Beacon TIM bit, whichcorresponds to the station's Association ID (AID), is set when theaccess point has frames buffered for the particular station.Accordingly, a station operating in power-save mode, which does not needto receive multicast/broadcast, may immediately return to sleep after itreceives a beacon with its TIM bit set “OFF”.

II. Multicast TIM Power-Save Mechanism

As will be appreciated by those skilled in the art, the above Proxy ARPmethod is useful for a VoIP client station that receives unicasttransmissions. A purely VoIP operating station greatly benefits from thelower power-consumption when using the Proxy ARP method described above.However, when the client station is both a VoIP station, as well as apaging station, the above method results in missed multicasts for thepaging application. For instance, if a dual-application station does notstay awake to receive power-save broadcast/multicast transmission, itwill miss IP multicast frames directed to the Paging Application. Thissection describes the present system and method whereby an access pointuses a Multicast Traffic Indication Message (MTIM) to indicate that ithas pending IP multicast frames buffered for stations in respectivepower-save multicast groups. For example, the access point 135, throughthe use of a MTIM, alerts stations 105, 110 and 115 in a power-savemulticast group 165 of buffered IP multicast frames.

It will be understood by those skilled in the art that an IP multicastgroup, such as IP groups 165 and 170 of FIG. 1, are identifiable by andassociated with a single IP multicast address. Furthermore, a one-to-onecorrespondence between IP multicast applications and IP multicastaddresses exists in most configurations and applications.

Referring now to FIG. 3, there is shown a flow chart of an embodiment ofthe methodology 300 adapted to incorporate a Multicast TrafficIndication Message into a multicast transmission network in accordancewith a disclosed embodiment. Initially, at step 305, the access pointobserves Internet Group Management Protocol (IGMP) Membership messagesfrom associated stations to determine membership in IP multicast groups.As will be appreciated by those skilled in the art, in the event that astation has roamed from a previous access point to a new access point,the new access point transmits an IGMP general query to solicitmembership reports, thereby identifying in which IP multicast groups theroaming station subscribes. Alternatively, group membership informationis stored, e.g., cached, in the network infrastructure and transferredto the new parent access point when a station roams using a contexttransfer protocol.

For example, the parent access point 135 IGMP Membership ReportMessages, sent by associated stations 105-120 to determine eachstation's membership in a specific IP multicast group, i.e, groups 165and 170. It will be understood by those skilled in the art that the useof two multicast groups is for exemplary purposes only and the subjectinvention is not limited solely to two groups. Alternatively, the accesspoint 135 is suitably capable of sending an IGMP general query tosolicit membership reports when a station (e.g. 105-120) roams from itshome BSS 140.

At step 310, the access point identifies stations corresponding to IPmulticast group registration. In other words, as described in theabove-identified related application, the system identifies specificmulticast groups and their corresponding member stations. The accesspoint then classifies each multicast group having an associated stationas to the type, such as active or power-save, of the identifiedmulticast groups at step 315. For example, once the IP multicast groups165, 170 are identified, the access point 135 classifies each IPmulticast group 165, 170 as active or power-save. A multicast group isclassified as active if all stations in the group are operating in802.11 active mode. Otherwise, an IP multicast group is classified aspower-save; e.g. if at least 1 client or station in the group isoperating in 802.11 power-save mode. It will be appreciated that theIEEE 802.11 specification defines the mechanics of an access point todetermine the active/power-save mode of associated stations.

Each multicast group having an associated station is then identified bythe access point as to type and number of associated stations at step320. Concurrently, at step 320 the type and station count of each IPmulticast group having an associated station is stored by the accesspoint. In reference to FIG. 1, the access point 135 stores the type,active or power-save, and station count for each IP multicast group 165,170. As well, the access point 135 stores a list of IP multicastaddresses for each associated station 105-120.

Next, the access point determines, at step 325 if the correspondingmulticast group station count is ‘0’. If a determination that thestation count is ‘0’ is made at step 325, the access point realizes thatit has no associated stations in the pre-identified multicast group, forexample as a result of disassociation of a station, and discards thesubject multicast message, or downlink IP multicast frames, at step 330.It will be appreciated that the station count for each multicast groupmay be incremented or decremented when any of the stations 105-120, in amulticast group 165 and 170 associates, disassociates, joins a multicastgroup, leaves a multicast group, or changes its power-save state.

When the access point determines at step 325 that the station count isgreater than ‘0’, the access point then determines, at step 330, if thetarget multicast group has all stations in a constantly active mode.When the access point determines all associated stations in the targetIP multicast group are in active mode, the access point immediatelyforwards the IP multicast/broadcast traffic at step 340 to the target IPmulticast group. In operation, the access point 135 immediately sends an1P multicast packet destined to an active multicast group 165, withoutwaiting for a DTIM beacon. If at step 335, the access point determinesthat at least one station in the target IP multicast group is operatingin power-save, the access point will buffer and queue themulticast/broadcast traffic at step 345. Thus, the access point 135buffers a multicast packet destined to a power-save multicast group 170,until the next DTIM beacon.

The system proceeds to step 350, where the access point determines if aDelivery Traffic Indication Message is due to be sent. If the time hasnot yet come for a DTIM Beacon to be sent, the access point returns tobuffering and queuing incoming IP multicast packets at step 345. When aDTIM Beacon is due to be transmitted by the access point at step 350,the access point transmits, at step 355, a DTIM Beacon including a MTIMelement.

The access point 135 includes a unique MTIM information element in eachDTIM Beacon. The MTIM functions to notify stations 120-130, in apower-save IP multicast group 170, to stay awake following a DTIM beaconin order to receive downlink multicast frames buffered for therespective group 170. The MTIM is also functioning to notify stations105-120 that the access point 135 supports the MTIM method, thusprompting stations 105-120 to selectively skip useless power-savemulticast/broadcast transmissions.

The MTIM element consists of a list of zero or more entries. The MTIMentries are capable of two alternative implementations. First, the MTIMlists pending multicast addresses for which downlink multicast framesare buffered in the access point 135. Thus, the stations, upon waking toreceive the DTIM/MTIM Beacon, review the list of pending addresses todetermine if any of the pending addresses correspond to an IP multicastaddress. Alternatively, the MTIM lists only those stations for whichdownlink multicast frames are buffered in the access point 135. Thus,the station, upon receipt of the DTIM/MTIM Beacon, reviews the list ofstations to determine if the station has pending multicast messages. Inthe preferred embodiment, an MTIM is structured exactly as an 802.11TIM. An MTIM consists of an array of bit flags, where each bit flagcorresponds to the Association Identifier (AID) of an associatedstation. An access point sets an MTIM bit for a station to “1” if thestation is a member of a multicast group and the access point has framesbuffered for that multicast group.

A VoIP/Paging station, 105-120, configured to support the Proxy ARP andMTIM mechanisms, wakes for each DTIM beacon. Moreover, such a station105-120 returns to sleep (e.g. power-save) immediately without receivinguseless downlink multicast/broadcast frames, if the station's TIM bit isrepresentative of an “OFF” state, and the station is not a member of amulticast group (e.g. 165, 170) identified by an entry in the MTIM.

One skilled in the art will appreciate that if an MTIM is comprised of alist of multicast addresses, then an MTIM entry is configured as an IPmulticast address or the corresponding multicast MAC address. It willfurther be understood by the skilled artisan that a multicast MACaddress, for an IP multicast group, is generated by concatenating a3-byte hex 01005E prefix with the low-order 3 bytes of the multicast IPaddress. Therefore, a station is capable of deriving the MAC addressfrom the IP address. Because Multicast MAC addresses are explicitlyenabled on client LAN interface cards (e.g. Ethernet or 802.11), it willfurther be appreciated that a management interface exists for a clientstation to determine multicast group membership.

It will be understood by those skilled in the art that the access pointprogramming and methodology, including logic and data structures, usedto support the MTIM mechanism are suitably identical to those needed tosupport active IP multicast groups, as discussed in the above-identifiedrelated United States patent application.

It will be understood by the skilled artisan that there is an infrequentneed to transmit “legitimate” broadcast packets for all associatedstations to receive. The AID 0 bit in the standard 802.11 TIM does notdistinguish between broadcast and multicast, so, with an MTIM present,the AID 0 bit indicates to the MTIM-aware client to monitor the MTIM forfurther information. In the event that an actual broadcast is intended,the AID 0 bit in the MTIM should be set to indicate the broadcast. Suchan indication would result in all MTIM-aware clients remaining awake toreceive the necessary broadcast. Setting the AID 0 bit in the MTIM ispreferable to just setting the all per-client MTIM bits, since the AID 0bit is insensitive to any transient IP multicast membership changes madeby the client.

Returning to FIG. 3, the system progresses to step 360, where adetermination is made that the station is a member of an IP multicastgroup identified by an entry in the MTIM. Upon this positivedetermination, the station remains in an active state, at step 375, toreceive the buffered IP multicast/broadcast traffic that the accesspoint has queued for transmittal. When it is determined at step 360 thatthe station is not identified by an entry in the MTIM, the stationverifies that the traffic indication message bit corresponding to thatstation is set to ‘OFF’ at step 365. When the traffic indication messagebit is set to ‘OFF’, the station returns to power-save protocoloperation at step 370. In the event that the traffic indication bit isnot set to ‘OFF’ at step 365, the station remains awake at step 375 toreceive the buffered IP multicast traffic. The skilled artisan willappreciate that if, upon receipt of the buffered IP multicast/broadcasttraffic, the station realizes it is not an intended recipient, thetraffic is discarded and the station will return to power-save protocoloperation.

The present methodology is capable of implementation by hardware,software or a combination of both. The subject invention need not and isnot intended to be limited to the embodiments described above. While thepresent method has been illustrated by the description of embodimentsthereof, and while the embodiments have been described in considerabledetail, it is not the intention of the applicants to restrict or in anyway limit the scope of the appended claims to such detail. Additionaladvantages and modifications will readily appear to those skilled in theart. Therefore, the system, in its broader aspects, is not limited tothe specific details, the representative apparatus, and illustrativeexamples shown and described. Accordingly, departures may be made fromsuch details without departing from the spirit or scope of theapplicant's general inventive concept.

1. A power-save method for a network having at least one access point and at least one associated power-save client comprising the steps of: buffering, at the access point, wireless data including at least one of a unicast frame and a multicast frame; transmitting a periodic scheduled beacon message over at least one wireless link, the beacon message including a unicast indication element and a multicast indication element; designating at least one beacon message as a multicast delivery beacon; transmitting the buffered multicast frame following the designated at least one multicast delivery beacon; determining multicast group membership for each associated client station; examining at least one Internet Group Management Protocol Membership Report; determining, from the at least one Internet Group Management Protocol Membership Report a multicast group membership for the associated client; and classifying each multicast group: wherein a multicast group is disabled when no associated clients are members, wherein a multicast group is active when all member stations are in active mode, and wherein a multicast group is power-save when at least one associated member station is in power-save mode.
 2. The method of claim 1, wherein the unicast indication element includes a unicast indicator, the unicast indicator instructing the client to remain awake to receive at least one unicast frame buffered in the access point; and the multicast indication element includes a multicast indicator, the multicast indicator instructing the client to remain awake, following a beacon transmission, to receive at least one multicast frame.
 3. The method of claim 2, wherein the unicast frame includes a destination MAC address identifying the client, and wherein the multicast frame includes a destination multicast address designating a multicast group of which the client is a member.
 4. The method of claim 3, wherein the multicast indication element further comprises a list having a plurality of entries.
 5. The method of claim 4, wherein each entry in the list corresponds to a multicast MAC address.
 6. The method of claim 4, wherein each entry in the list corresponds to a multicast IP address.
 7. The method of claim 4, wherein each entry in the list corresponds to a client identifier, wherein the client identifier identifies the client to receive the multicast frame following the transmission beacon.
 8. The method of claim 7, wherein the multicast indication element is structured as a standard 802.11 TIM element including an array of bit flags.
 9. The method of claim 8, wherein each bit flag of the array of bit flags corresponds to an 802.11 16-bit association identifier.
 10. The method of claim 9, further comprising the steps of: setting one of the bit flags in the array of bit flags to 0, wherein the setting of 0 is indicative to a client having the corresponding 16-bit association identifier to return to a power-save mode; and setting one of the bit flags in the array of bit flags to 1, wherein the setting of 1 is indicative to a client having the corresponding 16-bit association identifier to remain active to receive the multicast transmission.
 11. The method in claim 9 further comprising the step of setting a special bit flag in the array of bit flags to 1, wherein the setting of 1 is indicative to all associated clients to remain active to receive a multicast transmission.
 12. The method of claim 1, wherein the multicast indication element includes a special entry, the special entry indicating all associated clients are to remain awake following delivery of the beacon message.
 13. The method in claim 1, further comprising the step of omitting, from the beacon message, the multicast indication element, wherein the omission indicates to all clients to remain in an active mode.
 14. A power-save system for wireless data streaming, comprising: an access point configured to provide a wireless data link to at least one associated power-save client; means for buffering, at the access point, wireless data including at least one of a unicast frame and a multicast frame; means for transmitting a periodic scheduled beacon message over at least one wireless link, the beacon message including a unicast indication element and a multicast indication element; means for designating at least one beacon message as a multicast delivery beacon; means for transmitting the buffered multicast frame following the designated at least one multicast delivery beacon; means for operating a proxy Address Resolution Protocol service, wherein the power-save client does not need to remain awake following the multicast beacon transmission to receive a broadcast Address Resolution Protocol message; means for determining multicast cigroup membership for each associated client station: means for classifying each multicast group: wherein a multicast group is disabled when no associated clients are members, wherein a multicast group is active when all member stations are in active mode, and wherein a multicast group is power-save when at least one associated member station is in power-save mode; means for deleting multicast frames that are destined to the disabled multicast group; means for immediately transmittinci multicast frames that are destined to the active multicast group immediately; and means for buffering multicast frames destined to the power-save multicast group for transmission following a beacon transmission.
 15. The power-save system of claim 14, wherein the unicast indication element includes a unicast indicator, the unicast indicator instructing the client to remain awake to receive at least one unicast frame buffered in the access point; and the multicast indication element includes a multicast indicator, the multicast indicator instructing the client to remain awake, following a beacon transmission, to receive at least one multicast frame.
 16. The power-save system of claim 15, wherein the unicast frame includes a destination MAC address identifying the client, and wherein the multicast frame includes a destination multicast address designating a multicast group of which the client is a member.
 17. The power-save system of claim 16, wherein the multicast indication element further comprises a list having a plurality of entries, wherein each entry in the list corresponds to one of the group consisting of a multicast MAC address, a multicast IP address, and a client identifier.
 18. The power-save system of claim 17, wherein each bit flag of an array of bit flags in a TIM element corresponds to an 802.11 16-bit association identifier, further comprising: means for setting one of the bit flags in the array of bit flags to 0, wherein the setting of 0 is indicative to a client having the corresponding 16-bit association identifier to return to a power-save mode; means for setting one of the bit flags in the array of bit flags to 1, wherein the setting of 1 is indicative to a client having the corresponding 16-bit association identifier to remain active to receive the multicast transmission; and means for setting a special bit flag in the array of bit flags to 1, wherein the setting of 1 is indicative to all associated clients to remain active to receive a multicast transmission.
 19. The power-save system of claim 14, further comprising: means for examining at least one Internet Group Management Protocol Membership Report; and means for determining, from the at least one Internet Group Management Protocol Membership Report a multicast group membership for the associated client.
 20. A computer implemented power-save method for a network having at least one access point and at least one associated power-save client comprising the steps of: buffering, at the access point, wireless data including at least one of a unicast frame and a multicast frame; transmitting a periodic scheduled beacon message over at least one wireless link, the beacon message including a unicast indication element and a multicast indication element; designating at least one beacon message as a multicast delivery beacon; transmitting the buffered multicast frame following the designated at least one multicast delivery beacon; operating a proxy Address Resolution Protocol service, wherein the power-save client does not need to remain awake following the multicast beacon transmission to receive a broadcast Address Resolution Protocol message; determining multicast group membership for each associated client station; classifying each multicast group: wherein a multicast group is disabled when no associated clients are members, wherein a multicast group is active when all member stations are in active mode, and wherein a multicast group is power-save when at least one associated member station is in power-save mode; deleting multicast frames that are destined to the disabled multicast group; immediately transmitting multicast frames that are destined to the active multicast group immediately; and buffering multicast frames destined to the power-save multicast group for transmission following a beacon transmission.
 21. The computer implemented power-save method of claim 20, wherein the unicast indication element includes a unicast indicator, the unicast indicator instructing the client to remain awake to receive at least one unicast frame buffered in the access point; and the multicast indication element includes a multicast indicator, the multicast indicator instructing the client to remain awake, following a beacon transmission, to receive at least one multicast frame.
 22. The computer implemented power-save method of claim 21, wherein the unicast frame includes a destination MAC address identifying the client, and wherein the multicast frame includes a destination multicast address designating a multicast group of which the client is a member.
 23. The computer implemented power-save method of claim 22, wherein the multicast indication element further comprises a list having a plurality of entries, wherein each entry in the list corresponds to one of the group consisting of a multicast MAC address, a multicast IP address, and a client identifier.
 24. The computer implemented power-save method of claim 23, wherein each bit flag of an array of bit flags in a TIM element corresponds to an 802.11 16-bit association identifier, further comprising the steps of: setting one of the bit flags in the array of bit flags to 0, wherein the setting of 0 is indicative to a client having the corresponding 16-bit association identifier to return to a power-save mode; setting one of the bit flags in the array of bit flags to 1, wherein the setting of 1 is indicative to a client having the corresponding 16-bit association identifier to remain active to receive the multicast transmission; and setting a special bit flag in the array of bit flags to 1, wherein the setting of 1 is indicative to all associated clients to remain active to receive a multicast transmission.
 25. The method of claim 1, further comprising the steps of: deleting multicast frames that are destined to the disabled multicast group; immediately transmitting multicast frames that are destined to the active multicast group immediately; and buffering multicast frames destined to the power-save multicast group for transmission following a beacon transmission.
 26. The method of claim 25, wherein the multicast indication element includes information indicating frames are buffered for the power-save multicast group. 